The present invention relates to artificial joint system and to a method utilizing same capable of detecting the extent of relative displacement between an artificial joint member and a natural bone of the joint to which the artificial joint member is attached. More specifically, the present invention relates to an artificial joint system which includes a detection system capable of determining a distance between a joint member and reference points of the natural bone to which it is attached thereby enabling to determine the extent of relative displacement therebetween and the extent of deterioration of the natural bone of the joint. The present invention also relates to artificial joint system which includes a detection system for monitoring wear and displacement of articulating surfaces of the artificial joint members. Total joint artiroplasty is an operation involving the replacement of a damaged joint with an artificial joint assembly in order to restore motion to the joint and function to the muscles and ligaments and other soft tissue structures that operate and control the joint.
The operation is typically performed on individuals with a painful, disabling arthritic joint that is no longer responsive to conservative treatment regimens. This operation typically entails implantation of two or more artificial joint members into respective natural joint members so as to replace deteriorated natural articulating surfaces with artificial equivalents..
Artificial joint assemblies have been devised for a variety of joints including hips, knees, ankles, shoulders, elbows, and wrists (see, as examples, FIGS. 1a-k). Typically, components of artificial joints such as that shown in, for example, U.S. Pat. No. 4,068,342 to Townley et al. mimic the structure and function of joint members of a natural joint, thus providing as natural as possible articulation motion.
While artificial joint components are designed to provide stable and permanent attachment to the natural adjacent body tissue(s), at attachment interfaces, motion and/or loosening of the artificial joint member can occur, resulting in artificial joint relocation, which can lead to a loss of function, bone deterioration and tissue debris generation.
Such relocation can lead to an increase in wear to the articulating surfaces of the artificial joint. Such wear typically results in reduced function of the artificial joint and, in addition, produces joint debris which are expelled from the joint area to the surrounding tissues and may cause adverse reactions, such as inflammatory granulatoma, in these tissues.
The debris expelled from the artificial joint includes microscopic particles typically measuring up to a few microns in size. These particles provoke various tissue reactions, which affect the bones hosting the artificial joint implant.
The type and severity of the biological reaction to wear generated particles depend mainly on the physical properties and to a lesser degree also on the chemical properties of the wear particles. For example, in joints which include polyethylene component three types of particles are observed, chunks, flakes and granules. The granules, which are approximately one micron in size, are responsible for an intense inflammatory reaction. The histology is characterized by phagocytosis of the particles, resulting in large conglomerations of macrophages due to their inability to digest the polyethylene. The inflammatory process is accompanied by release of biochemical mediators such as prostaglandins and interleukins that cause absorption of the host native bone. Wear particles of other plastics, such as acetyl-copolymer, are of similar physical shapes but may cause an even more intense reaction.
Wear in metallic and ceramic joints is typically characterized by small granules which are taken in by macrophages, leading to a similar biochemical reaction to that caused by plastics.
As a wear of a joint progresses and larger amount of particles are expelled to the surrounding tissues, further bone absorption and loosening of the joint implant may occur. Such loosening of a prosthetic joint implant and damage to surrounding tissues is often left undetected in a patient even if regularly checked by a physician. Most modern methods currently employed for determining the extent of loosening and/or wear of an artificial joint, rely upon either X-ray, computer tomography, isotope bone scan or magnetic resonance to image the implanted joint and are of insufficient accuracy or technically difficult to perform and/or interpret even by highly skilled professionals. In fact, the most modern joint replacement assemblies incorporate metal backed plastic components, metallic components, or ceramic components within metallic shells and as such the available imaging methods cannot produce sufficient contrast in order to determine artificial joint loosening and/or articulating surface wear.
As a result of inefficient detection methods, oftentimes the only indication of early joint loosening is the pain and discomfort suffered by the patient. Oftentimes bone absorption progresses to a stage necessitating replacement surgery using larger implants, and/or bone grafts to accommodate for the lost bone tissue. The prognosis for success and service life of the implant after such a corrective operation is less predictable and depends, among other factors, on the extent of bone absorption suffered. If performed relatively early on, such corrective surgery has an increased chance of success. Therefore, a method to detect the extent and depth of wear of the articulating surfaces of an artificial joint is of paramount importance both to the patient and the treating physician.
There is thus a widely recognized need for, and it would be highly advantageous to have, an artificial joint system which enables to monitor relative displacement of artificial joint members and wear to the articulating surfaces thereof, thus enabling a treating physician to detect joint loosening in an individual prior to bone deterioration and absorption and significant damage to articulating surfaces.